Projection technology utilizes several technologies for projecting images at high resolution. Projection technologies may be categorized into two broad categories. One category may be transmittive projection system that includes technologies utilizing cathode ray tubes (CRTs) or liquid crystal displays (LCDs). Another category may be reflective projection system that includes technologies utilizing microelectromechanical systems (MEMS), such as digital micromirror devices (DMD™) or digital light processing (DLP). More recently, reflective projection systems include liquid crystal on silicon (LCOS) technology. Commonly, some of the issues associated with these projection systems are issues such as resolution, cost, manufacturability, and size, to name a few.
In transmittive projection systems, the advent of thin film transistors (TFTs) has improved the technology in particular, transmittive projection technology associated with LCDs. However, as the LCDs are reduced in size, the TFTs may start to interfere with the transmission of light through the LCDs because as the LCDs are reduced in size, the TFTs occupy relatively more space (i.e., the aperture ratio decreases as the resolution increases).
Reflective projection systems do not have the concern of light interfering with TFTs because light is reflected rather than transmitted through the LCD. However, utilization of MEMS technology can be costly because of the technical requirements associated with such small mechanical devices that may range in size of 16 square micrometers (i.e., manufacturing and controlling such small mechanical objects). In reflective projection systems, a technology utilized to address some of the issues associated with MEMS technology is the liquid crystal on silicon (LCOS) technology. The LCOS technology integrates liquid crystal technology and a metal oxide semiconductor (MOS) to result in a reflective projection system that offers high resolution, low cost, scalable to small sizes, and relatively easy to manufacture.
An aspect of utilizing LCOS projection systems involves management of light within the projection system. For example, the management of light may involve processes such separating light into its various color components, polarizing, and recombining the various color components to form an appropriate image. An example of light management device, which may be referred to as an architecture, suitable for the LCOS projection system may be a ColorQuad™ architecture utilizing ColorSelect™ polarization filter technology by Colorlink, Inc. of Boulder, Colo.
The ColorQuad™ architecture selectively rotates the polarization of one color relative to its complement. Utilizing the ColorSelect™ polarization filter technology, including polarizing beamsplitter (PBS) cubes, the ColorQuad™ architecture facilitates high contrast displays by providing polarization integrity of color separation and recombination.
Because light commonly used in a projection system is non-coherent light (i.e., white light), management of light may be difficult due to many factors. One factor, in particular, is straying of light.
For example, the PBS cubes used to manage light in an LCOS projection system can be arranged in a very compact manner by having PBS cubes of various sizes cemented together. To properly manage the light in the PBS cubes, various lenses, filters, and reflective coatings are utilized. However, the non-coherent nature of light combined with the compact arrangement of the PBS cubes, can result in stray light contaminating the projected image.
Even though, the LCOS technology offers high resolution, low cost, scalable to small sizes, etc., the non-coherent nature of the light used and the compact arrangement of the PBS cubes within the reflective projection system, can result in stray light contaminating the projected image, thereby decreasing contrast and introducing image homogeneity issues.